1. Technical Field of the Invention
This invention relates to removal of coating material from a coated substrate. More particularly, this invention relates to the selective removal of photosensitive coating material from the periphery of a substrate or wafer used to produce micro integrated circuit chips.
2. Background Art
In the production of micro integrated circuit components or "chips" it is customary to coat a wafer or substrate with a photosensitive material and then expose the coated substrate to a light source imaged through a pattern or mask. Portions of the coating exposed to the light source become chemically altered to permit selective removal of either the exposed portion of the coating or the unexposed portion by a solvent.
The resultant selectively exposed substrate is then subjected to further processing steps, such as etching, diffusion, plating or the like, to provide the layers of microcircuitry which will eventually result in the production of a number of integrated circuits or chips on the substrate.
Because of the minute spacing between circuit components and conductor paths, introduction of foreign particles, such as dust or the like, is scrupulously avoided. A single particle of dust on the substrate, for example, may result in the malfunction and, therefore, loss of one of the chips on the substrate. A number of such foreign particles on a substrate may therefore result in a serious decrease in the yield from the wafer or substrate.
Recently it has been noted that some of these losses apparently occur due to the presence of particles of photoresist coating not exposed to light on portions of the coating where the coating has been exposed to light, i.e., not corresponding to the desired light pattern imaged on the coating. The presence of such particles can therefore result in irregularities producing defects in the particular chips on the substrate where these particles lodge.
The photoresist coating material is customarily applied as a liquid to the center of a spinning circular substrate and is evenly spread across the surface by centrifugal forces. A slight amount of the coating flows over the end edge of the substrate and onto the periphery of the lower surface. This portion of the coating is usually not as uniform.
Microscopic examination of the uneven surfaces of the loose particles of photoresist coating noted above indicate that one source of such particles is apparently the end edges of the substrate. It has been surmised that the presence of these particles is the result of handling of the substrates during processing which may result in the dislodgment or flaking off of the coating adjacent the periphery of the coated substrate with at least some of the dislodged particles becoming inadvertently scattered over the remainder of the coated substrate resulting in eventual defects.